arsenic removal in drinking water by reverse
osmosis.
md. fayej ahmad
Department of mathematical science and tecnology
Master Thesis 30 credits 2012
PREFACE
This is my 30 credits Master thesis in the Department of Mathematical Science and Technology.
I am a Master’s student in the Department of Plant and Environmental Science. My Masters
program is Environment and Natural Resources. Specialization Sustainable Water and
Sanitation, Health and Developmentat the Norwegian University of Life Sciences (UMB).
First, I would like to thank my supervisor Professor Harsha Ratnaweera at the Norwegian
University of Life Sciences, for his valuable advice, comments, great support and progressive
ideas for the improvement of the thesis. He is really a great and generous person in my eyes.
I would also like to thank my Co-supervisor Georg Finsrud for his valuable advice and for his
optimism and enthusiasm.
Further, I would like to thank Karl Andreas Jensen, Chief Engineer at the Department of Plant
and Environmental Science for his help in laboratory work and also Lelum Manamperuma a PhD
student in the Mathematical Sciences and Technology Department for his help and good
company.
Thanks a lot.
Ås, March 2012
Md.Fayej Ahmad. i Abstract:
Arsenic is widely distributed in nature in the air, water and soil. Acute and chronic arsenic
exposure by drinking water has been reported in many countries, especially Argentina,
Bangladesh, India, Mexico, Mongolia, Thailand and Taiwan. There are many techniques used to
remove arsenic from drinking water. Among them reverse osmosis is widely used. Therefore the
purpose of this study is to find the conditions favorable for removal of arsenic from drinking
water by using reverse osmosis techniques. The experiments were conducted with two types of
arsenic (III, V) in tap water up to arsenic concentration of 400 µg/l. We were applied different
production water flow rates and pH for removal of arsenic from drinking water. We conclude
that in this experiment 99% removal efficiency was achieved for arsenic (III) and arsenic (V).
Arsenic (V) is very efficiently removed by reverse osmosis and arsenic (III) removal efficiency
depends on water pH. Practical processes can be developed with reverse osmosis to remove all
major species of arsenic from water.
ii Contents
1. Introduction………………………………………………………..................... 1
2.ChemistryandGeochemistryofarsenic………………………………...............
2
3.Natural distribution of arsenic………………………………………………..
4.The effects of arsenic on human health………………………………………
6
10
4.1 Skin Cancer…………………………………………………………….. 12
4.2 Lung cancer………………………………………………………………. 12
4.3 Effects on memory and intellectual function…………………………..
12
4.4 Reproductive effects…………………………………………………....
12
5. Problem and remediation methods of arsenic removal from drinking
water……………………………………………………………………………….
6. Different membrane use for water treatment………………………………
13
14
6.1 Ultrafiltration…………………………………………………………..
14
6.2 Microfiltration…………………………………………………………
15
6.3 Nanofiltration…………………………………………………………... 15
6.4 Reverse Osmosis System……………………………………………….
7. Materials, methods and experimental design……………………………….
7.1 Description of membrane that use in experiment………………………
16
18
23
7.2 Statistical analysis……………………………………………………… 24
7.3 Materials use for experiment.................................................................... 24
8. Results…………………………………………………………………………….
9. Discussion…………………………………………………………………………
10 Conclusion……………………………………………………………………..
25
30
32
References…………………………………………………………………………… 33
Appendix index……………………………………………………………………..
iii 35
1. Introduction
Water is the most essential element for life. In many parts of the world people suffer from poor
drinking water quality. Especially people in developing countries are suffer because of the lack
of pure drinking water. This is why people are at risk of health hazard (Nguyen, 2007). Arsenic
contamination in drinking water is one of the most prominent problems in some countries of the
world. Arsenic is generally distributed in the environment (air, water and soil). Arsenic
distribution in nature is in both organic and inorganic form. Arsenic has a dual nature. It is a
useful element for human health and, on the other hand, if the concentration is higher than the
expected limit, arsenic creates problems for health. Arsenic is used for different purposes in the
commercial sector. Sources of arsenic in drinking water originate largely from natural sources
and create health problems in some countries in the world (Ning, 2002).
The World Health Organization (WHO) has suggested that the upper limit of
arsenic in
drinking water should be set to 10 µg/l as an alternative to 50 µg/l (Nguyen, 2007). Acute and
chronic health effects by arsenic in drinking water have been reported in different countries,
especially Bangladesh, India, Mexico, Argentina, Mongolia, Thailand and Taiwan. In these
countries a large part of the groundwater is contaminated by arsenic, this groundwater is a
source of drinking water (Ning, 2002). The concentration of arsenic in groundwater is 100 to
over 2000 µg/l. Some studies show that long term drinking of arsenic contaminated groundwater
can lead to cancer of the bladder, lungs, skin, kidney, nose and liver. Long time exposure to
arsenic has non cancer effects. It damages cardio- vascular, pulmonary, immunological and
neurological systems. Arsenic is an environmental toxicant in drinking water (Ning, 2002).
Bangladesh is one of the most arsenic affected countries in the world, 50 million out of 140
million people are affected by arsenic by drinking water highly concentrated with arsenic from
tube wells and dug wells (Geucke et al., 2008). In Bangladesh the arsenic concentration in
ground water is up to 1000 µg/l. Because of arsenicosis present and future generations in the
Bangladeshi population are exposed to health risks (Geucke et al., 2008).
In the present era, tecnology developments allow arsenic to be removed from drinking water.
Among the most commonly used technologies are oxidation, co-precipitation, adsorption onto
coagulation flocks, lime treatment, sorption media, ion exchange resin and membrane technology
1 (Geucke et al., 2008). Membrane technology has advanced enormously for water treatment all
over the world. Reverse osmosis (RO) membranes have became recognized as one of the best
available technologies for cleaning inorganic hazard in water (Kang, 2000).
2. Chemistry and Geochemistry of arsenic:
Arsenic, atomic number 33, belongs to the VB group in the periodic table. Arsenic is a metalloid,
and in occurs in various oxidation states (-III, 0, +III and +V) in nature. In natural water, arsenic
is mostly found in inorganic forms as tri-valent arsenite arsenic (III) and penta valent arsenate
arsenic (V) (Nguyen, 2007).
The arsenic commonly present in water is the pH dependent species of arsenic (H3AsO4) and the
arsenous (H3AsO3) acid system. These anions have acidic characteristics. The stability and
dominance of a specific species depends on the pH of the solution. Arsenate are stable in aerobic
or oxidizing condition,while arsenites are stable under anaerobic or reducing condition (Figure 1)
Figure 1: Potential pH diagram for the arsenic water system at unit activity of all species
(Choong et al., 2007)
2 The concentration of arsenic in the earth's crust normally ranges from 1.5 - 5 mg/kg. Table 1
illustrates arsenic minerals in nature. Arsenopyrite, realgar, and orpiment minerals contain
sulfide ores such as copper, lead, silver, and gold. The weathering process may release arsenic
from sulfide ores in soil, surface water, groundwater and the atmosphere (Ning, 2002).
Table 1. Major arsenic minerals commonly found in nature. (Gomez-Caminero et al.,
2001).
Mineral
Composition
Occurrence
Native arsenic
As
Proustite
Ag3AsS3
Rammelsbergite
NiAs2
Safflorite
(Co, Fe)As2
Generally in mesothermal vein deposits
Seligmannite
PbCuAsS3
Occurs in hydrothermal veins
Smaltite
CoAs2
Niccolite
NiAs
Vein deposits and norites
Realgar
AsS
Vein deposits, often associated with orpiment,
clays and limestones, deposits from hot
springs
Orpiment
As2S3
Hydrothermal veins, hot springs, volcanic
sublimation product
Cobaltite
CoAsS
High-temperature
rocks
Arsenopyrite
FeAsS
The most abundant Arsenic
dominantly mineral veins
Tennantite
(Cu,Fe)12As4S13
Hydrothermal veins
Enargite
Cu3AsS4
Hydrothermal veins
Arsenolite
As2O3
Claudetite
As2O3
Scorodite
FeAsO42H2O
Annabergite
(Ni,Co)3(AsO4)2·8H2O
Hydrothermal veins
Generally one of the late Ag minerals in the
sequence of primary deposition
Commonly in mesothermal vein deposits
metamorphic
mineral,
Secondary mineral formed by oxidation of
arsenopyrite, native arsenic and other As
minerals
Secondary mineral formed by oxidation of
realgar, arsenopyrite and other As minerals
Secondary mineral
Secondary mineral
3 deposits,
Hoernesite
Mg3(AsO4)2·8H2O
Secondary mineral, smelter wastes
Haematolite
(Mn,Mg)4Al(AsO4)
Conichalcite
Adamite
CaCu(AsO4)(OH)
Zn2(OH)(AsO4)
Domeykite
Cu3As
Found in vein and replacement deposits
formed at moderate temperatures
Loellingite
FeAs2
Found in mesothermal vein deposits
Pharmacosiderite
Fe3(AsO4)2(OH)3·5H2O
Secondary mineral
Secondary mineral
Oxidation product of arsenopyrite and other
As minerals
The arsenic concentration in soil naturally ranges from 0.1 to 40 mg/kg, and the average
concentration range from 5 to 6 mg/kg. Arsenic contaminates groundwater and surface water
through processes such as erosion, dissolution and weathering (Figure 2). The geothermal
process is also responsible for arsenic contamination in groundwater. Other natural sources that
influence arsenic contamination include volcanic eruptions and forest fires. Volcanic activity is
the principal natural source of arsenic emissions to the atmosphere, and it is predicted that 2,800
to 44,000 metric tons of arsenic emissions released due to volcanic activity annually (Ning,
2002).
4 Figure 2. Arsenic cycle in the environment source (Saha, 2002).
Arsenic (V) and arsenic (III) are the most common forms of arsenic in ground and surface water.
Different inorganic forms of arsenic oxides occur naturally in the environment (As2O3, As2O5)
and sulfides ( As2S3, AsS, HAsS2, HAsS33-). The inorganic forms of arsenic that are stable in
oxygenated waters include arsenic acid As (V) species (H3AsO4, H3AsO4-, H3AsO42- and AsO43).
In arsenic acid arsenic (III) is also stable as H3AsO3 and H2AsO3- under slightly reducing
aqueous conditions. Arsenic transportation depends on different factors such as the oxidation
state, pH, iron concentration, metal sulfide, sulfide concentration, oxidation and reduction
potential, temperature, salinity and distribution and composition of biota (Ning, 2002). Arsenic
concentration in surface water depends on some additional factors which include total suspended
sediment, seasonal water flow volumes, time and day (Ning, 2002).
5 Sorption chemistry is also responsible for transportation of arsenic in surface water systems. If
the pH and arsenic concentration in the water is high and the concentration of total suspended
solids is low, the sorption process may be less important. On the other hand, pH, arsenic
concentration is low and suspended sediment load is high arsenic present in suspended particle
phase than dissolved phase. Arsenic is dispersed by wind and high flow scouring. "Diurnal
changes as much as 21 % of arsenic concentration have been observed in river attributable to pH
changes due to sunlight and photo synthesis" (Ning, 2002).
3. Natural distribution of arsenic:
Arsenic is the 20th richest element in the earth crust, and the 14th in sea water. Arsenic is an
extraordinary crystal element comprising about five hundred thousandths of 1% (0.00005%) of
the earth crust. The arsenic concentration in igneous and sedimentary rock is 2 mg/kg with
different types of rocks containing different concentrations. Ranges from 0.5 - 2.5 mg/kg and
higher concentrations were found in argillaceous sediments and phosphorites. Arsenic has been
found to reduce marine sediment and may also co-precipitate with ironhydroxides and sulfides in
sedimentary rock. Table 2 shows arsenic concentrations in some natural geochemical materials
(Mandal and Suzuki, 2002).
Over 200 different minerals contain arsenic, of which 60% are arsenates, 20% sulfides and
sulfosalts and another 20% are arsenides, arsenates, silicates and elemental arsenic. Arsenic
concentration is categorized into three major classes: Igneous, Sedimentary and Metamorphic
rock (Table 2).
Table 2. Arsenic concentration in the three most common rock worldwide (Mandal and
Suzuki, 2002).
Materials
Igneous
Acidic
Rhyolite (extrusive)
Arsenic (mg/kg)
3.2–5.4
Granite (intrusive
0.18–15
Intermediate
Latite, andesite,
trachyte (extrusive)
0.5–5.8
Materials
Sedimentary rocks
Marine
Shale/claystone
(nearshore)
Shale/claystone
(offshore)
Carbonates
Phosphorites
6 Arsenic (mg/kg)
4.0–25
3.0–490
0.1–20.1
0.4–188
Diorite, granodiorite,
syenite (intrusive)
Basic
Basalt (extrusive)
Gabbro (intrusive)
Ultrabasic
0.09–13.4
Sandstone
0.6–9
Peridotite, dunite,
serpentinite
Metamorphic rocks
Quartzite
Slate/phyllite
0.3–15.8
Non-marine
Shales
Claystone
Recent sediments
(marine)
Lake
2.2–7.6
0.5–143
Clays
Carbonate
Stream/river
Schist/gneiss
0.0–18.5
Soils
0.18–113
0.06–28
3.0–12
3.0–10
2.0–300
4.0–20
<1.0
5.0–4000 (mineralized
area)
<0.1–97
Table 3. Arsenic deposits in the world (Gomez-Caminero et al., 2001).
Type of deposits
Arsenic mineral
Enargite-bearing
copper–zinc–lead
deposits
Enargite
Arsenical pyritic
copper deposits
Arsenopyrite,
tennantite
40,000 (4%)
Native silver and
nickel–cobalt
arsenide bearing
deposits
Smaltite,
domeykite,
safflorite,
rammelsbergite,co
baltite,niccolite,
loellingite,
arsenopyroe,
Arsenopyrite,
loellingite
25,000 (2.5%)
Realgar, orpiment
2000 (0.2%)
Arsenopyrite
2000 (0.2%)
Arsenical gold
deposits
Arsenic sulfide and
arsenic sulfide gold
deposits
Arsenical tin deposits
Average
arsenic
concentrati on
(mg/kg)
1000 (0.1%)
<5000 (0.5%)
7 Location
United States, Argentina, Chile,
Peru, Mexico, Republic of the
Philippines, Spain, Yugoslavia,
USSR
United States, Sweden, Federal
Republic of Germany,
Japan,Bangladesh
France, USSR
Canada, Norway, Germany,
Democratic Republic,
Czechoslovakia
Unites States, Brazil, Canada,
Republic of South Africa,
Australia,
USSR
United States, People’s
Republic of China
United States, Bolivia,
Australia,
Indonesia, Malaysia, Republic
Arsenical quartz,
silver and lead–zinc
deposits
Arsenopyrite
6000 (0.6%)
of
South Africa
United States, Canada, et al.
Arsenic is found in fresh and groundwater in many countries around the world (Mandal and
Suzuki, 2002). The concentration of arsenic varies in ground water across the globe (Table 4).
The WHO has recommended that the maximum concentration should not exceed 10 µg/l. Sea
water contains arsenic concentrations from 0.001 - 0.008 mg/l. Table 4 shows arsenic affected
countries, sources of arsenic and concentrations of arsenic in water (Mandal and Suzuki, 2002).
Table 4. Concentrations of arsenic in groundwater of the arsenic-affected countries
(Mandal and Suzuki, 2002).
Location
South-West Finland
New Jersey, USA
Western USA
South-west USA
Bangladesh
Lagunera region, northern
Mexico
Shanxi, PR China
Calcutta, India
Fukuoka, Japan
Arsenic source
Well waters; natural origin
Well waters
Geochemical environments
Alluvial aquifers
Well waters
Well waters
Concentration (µg/l)
17–980
1 (median) 1160 (maximum)
48,000 (maximum)
16–62
10 -1000
8–624
Well waters
Near pesticide production
plant
Natural origin
0.03–1.41
<50–23,080
0.001–0.293
In addition to geochemical factors, microbial agents can influence the oxidation state of arsenic
in water. Different geochemical processes can transfer arsenic in aquatic systems. Table 5
describes arsenic concentration in different environmental media.
Table 5: Arsenic concentration in environmental media (Ning, 2002).
Environmental media
Arsenic concentration range
Air ng/m3
1.5-53
Rain from unpolluted ocen air µg/l
0.019
Rain from terrestrial air µg/l
0.46
8 Rivers µg/l
0.20-264
Lakes µg/l
0.38-1000
Ground well water µg/l
<1.0- >1000
Sea water µg/l
0.15-60
Soil mg/kg
0.1-1000
Stream /river sediment mg/kg
5.0-4000
Lake sediment mg/kg
2.0-300
Igneous rock mg/kg
0.3-113
Metamorphic Rock
0.0 -143
Sedimentary Rock
0.1-490
Biota(green algae) mg/kg
0.5-5.0
Arsenic is present in air, it exists in nature mainly absorbed on particulate matter. Arsenic in air
is normally a mixture of arsenite and arsenate. The organic arsenic percentage in the air is very
low except in areas of arsenic pesticide application (Mandal and Suzuki, 2002). Human exposure
by arsenic is very low, normally the arsenic concentration in air is 0.4-30 ng/m3. The United
States Environmental Protection Agency (USEPA) estimated that the average exposure in the
United States (U.S) was 6 ng As/m3. Arsenic concentration depends on the particulate matter and
relative vapor. In Europe, the arsenic concentration in the air is very low. Concentration depends
on the region: 0.2 - 1.5 ng/m3 in rural areas, 0.5 - 3.0 ng/m3 in urban areas, and not higher than
50 ng/m3in industrial areas (Mandal and Suzuki, 2002).
In Bangladesh, groundwater contains high amounts of arsenic (50-2000 µg/l) and has created a
serious health hazard in human history. (Mandal and Suzuki, 2002). Figure 3 shows that arsenic
comes from different sources (Aquifer, geothermal, coal, mining) and the amount of the global
population at risk.
9 Figure 3: Sources of arsenic and people living under risk of arsenic contaminated water (Garelick
and Jones, 2008).
4. The effects of arsenic on human health:
Human exposed to arsenic through ingestion, inhalation, or skin absorption. High doses of
arsenic may have acute toxic effects give gastrointestinal symptoms (poor appetite, vomiting,
and diarrhea) and disturbed the fractions of the cardiovascular and nerve systems(Safiuddin,
2001).
The data collected by the department of public health , Non government organizations (NGOs)
and private organizations have revealed that a large part of the population in Bangladesh are
suffering from melanosis, leuco melanosis, keratosis, hyperkeratosis, gangrene and skin cancer
(Safiuddin, 2001). Malanosis (93.5%) and caratosis (68.3%) are the most common diseases.
Leuco-malanosis (39.1%) and hyper keratosis (37.6%) have been found in many cases
(Safiuddin, 2001).
The extend of arsenic intoxicion depends on the type of arsenic compounds and concentration of
arsenic in the human body (Safiuddin, 2001). It has been reported that 40 to 50 % of the ingested
arsenic be retained in human body. The amount of arsenic contaminated water is very high in
10 Bangladesh, mainly in the rural areas. In Bangladesh most of the people live in rural areas, where
the average water consumption is 5 liters per person/day. They also use arsenic contaminated
water for cooking. Around 90 % of people have arsenic in their nail, hair, and urine above the
normal level present in Table 6 (Safiuddin, 2001).
Table 6. Arsenic level in hair, nails, skin scales and urine of among Bangladeshi rural area
people (Safiuddin, 2001).
Field Survey from August 1995 to February 2000
Total Hair Samples Collected from 210 Arsenic Affected Villages
Percentage of Samples Having Arsenic above Toxic Level
Total Nail Samples Collected from 210 Arsenic Affected Villages
Percentage of Samples Containing Arsenic above Normal Level
Total Urine Samples Collected from 20 Arsenic Affected Villages
Percentage of Samples Having Arsenic above Normal Level
Total Samples of Skin Scales
4386
83.15%
4321
93.77%
1084
95.11%
705
Percentage of Samples Containing Arsenic above Toxic Level
97.44%
Field Survey from April 1999 to February 2000 (27 Days)
Total Hair Samples
1054
Percentage of Hair Samples Having Arsenic above Toxic Level
89.35%
Total Nail Samples
1000
Percentage of Nail Samples Containing Arsenic above Normal Level
94%
Total Urine Samples
41
Percentage of Urine Samples Having Arsenic above Normal Level
Total Samples of Skin Scales
115
Percentage of Samples Containing Arsenic above Toxic Level
11 97.50%
100%
4.1 Skin Cancer
A significant relationship between skin cancer and arsenic exposure has been observed
(Rossman, 2004). The mechanism of action may involve effects on DNA methylation and DNA
repair. It is associated with cancer of the skin and internal organs, as well as vascular disease
(Rossman et al., 2004).
4.2 Lung cancer
Lung cancer significantly increases with increased arsenic concentration in the body. Together
with cigarette smoking arsenic exposure has a synergistic effect thus increasing the risk of lung
cancer. An increased risk of lung cancer was associated with the high level of arsenic exposure
via drinking water. Research revealed a decreased level of arsenic exposure also reduced lung
cancer among smokers; the mortality rate of lung cancer reduces when arsenic concentration is
lessened in drinking water (Hopenhayn-Rich et al., 1998).
4.3 Effects on memory and intellectual function
The level of arsenic concentration in urine sample among Mexican children was inversely
associated with Verbal intelligence quotient and long term memory. This study found an impact
on long term memory and understanding capability of children. Children who drank water with
an arsenic concentration of 50 mg/l have a lower performance of intellectual capability than
children who drank water containing 5.5 mg/l of arsenic (Wasserman et al., 2004).
4.4 Reproductive effects
Pregnancy complications are found due to chronic effects from ground water contamination with
arsenic. A study found a positive correlation with arsenic concentration and fetal loss and pre
mature delivery. Women who chronic exposure drank (less than 50 µg/l) arsenic in drinking
water gave birth to children with a decrease birth weight (Chen et al., 2004).
12 Figure 4: Skin lesions in soles and hands due to arsenic poisoning from drinking water (Safiuddin, 2001)
Skin ailments such as those displayed in figure 4 are generally symptoms of continuous drinking
of arsenic contaminated water and are symptoms of different skin diseases like
hypopigmentation (white spots on the skin), hyper pigmentation (dark spot on the skin), keratosis
and melanonin. More serious health problems such as skin cancer or cardiovascular and nervous
affections are known to appear with a latency of 10 or more years (Zürich, 2007).
5. Problem and remediation methods of arsenic removal from drinking
water:
Arsenic concentration in drinking water is different from place to place. In developing countries
it is very expensive to remove arsenic from drinking water by central water treatment systems.
People living in rural areas are mostly affected by arsenic contaminated in drinking water
because of poor treatment facilities. Different technologies have been developed to remove
arsenic from drinking water. Some technologies are not suitable for safe drinking water supply in
small communities because of expensive have too maintenance costs.
Membrane technology is relatively new for water treatment. It is convenient for small and large
scale water treatment facilities. In our experiment we use reverse osmosis system for arsenic
water treatment and investigate to find out optimal conditions for better removal efficiency.
Reverse osmosis systems can be prepared for small and large scale treatment unit with different
13 membranes. Reverse osmosis systems are very easy to operate, having low maintenance costs
and can be used as a small scale treatment plant in rural areas.
6. Different membrane use for water treatment:
6.1 Ultrafiltration:
Ultrafiltration has been using for many different applications, including the field of drinking
water treatment. It has used to remove pathogenic microorganisms, bacteria, viruses, colloids,
turbidity, soluble macromolecules and natural organic matter. Ultrafiltration is used in lieu of
coagulation/precipitation and media filtration pretreatment for reverse osmosis and nano
filtration membranes (Segal and Dosoretz, 2011).
Supplying clean and, drinking water is an emerging challenge. Pollution originates from industry
and commercial sources. Ultrafiltration has widely used for water treatment all over the world
(Hank and Wyckoff, 2010).
Advantages of ultrafiltration (Hank and Wyckoff, 2010):
•
Remove pathogen and turbidity in only one treatment step.
•
Complete obstacle for bacteria, virus and parasites.
•
Deactivated pathogens are fully removed in the water.
•
Low operating effort: ultrafiltration systems made for small water treatment solutions
are fully automated.
•
Combined with activated carbon pre-filtration, it removes taste, odor, pesticides and
residuals of antibiotics.
•
Green technology: some ultrafiltration can be directly operated on solar power.
•
No chemicals application to the water.
14 6.2 Microfiltration:
Microfiltration removes contaminants from the fluid micro porous membrane. The normal
microfiltration porous range is 0.1 - 10 (µm). Micro filtration is different from nanofiltration
and reverse osmosis. Water passes through the membrane with low pressure to high pressure in
two systems. Microfiltration is normally used for drinking water treatment. It effectively
remove major pathogens and contaminants such as Giardia lamblia cysts, cryptosporidium and
large bacteria. For this application the filter has to be rated for 0.2 µm or less (Dharmappa and
Hagare, 1999).
Advantages of microfiltration for water treatment (Dharmappa and Hagare, 1999).
•
Bacterial decontamination with little or no chemical addition.
•
Water treatment system is very compact.
•
Ultra pure water is used for industrial purposes.
•
Microfiltration water treatment system might be economical for small water treatment
system.
•
In some different cases sludge treatment can be considerably lowest amount.
•
High and stable product water quality.
6.3 Nanofiltration:
Nanofiltration membranes can remove different valence ions and different molecular weight
organic molecules from the water, it depends on membrane charge and pore size.
Nanofiltration is used for purification, biochemical substance separation, waste water
reclamation and water softening (Ji et al., 2011).
Nanofiltration membrane charged both positively and, negatively. Nanofiltration membranes
are made from polyamids, sulfonated polysulfone and sulfonated polyphenyleneoxides. This
compounds have used for negatively charged membrane. Positively charge membrane is
more effective in removing multi-valent cations and remove amino acids below their
isoelectric point. Positively charged Nanofiltration have been developed in recent years (Ji et
al., 2011).
15 6.4 Reverse Osmosis System:
Reverse osmosis is commonly used to reduce suspended solid particles and dissolved matter
from water. Table 7 shows the common contaminants removed by reverse osmosis, including
harmful pesticides (Dvorak, 2008)
Table 7. Common contaminants removal by reverse osmosis system (Dvorak, 2008).
Ions and metals
Arsenic,aluminum,barium,cadmium,calcium,chlorine,chromium,copper,
fluoride,iron,lead,magnesium,manganese,mercury,nitrate,potassium,
radium, selenium, silver, sodium, sulfate, zinc
Particles
Asbestos, protozoan cysts, cryptosporidium
Pesticides
Endrin, heptachlor. lindane, pentachlorophenol
Not all contaminants can be removed by reverse osmosis. Dissolved gases like hydrogen
sulfide, will pass through the membrane. Some pesticides, solvents and volatile organic
chemical compounds cannot be removed by a reverse osmosis system. Removal efficiency of
reverse osmosis depends on the concentration of the contaminants and chemical properties,
characteristics of the membrane and operating system of the reverse osmosis system (Dvorak,
2008).
Reverse osmosis system contain two solutions of different chemical concentrations separated
by a semi permeable membrane. Water passes through the membrane from the dilute to the
more concentrated solution due to a different pressure level. This pressure is called osmotic
pressure and the process is called osmosis (Dvorak, 2008).
In a reverse osmosis system, pressure is applied to the concentrated side of the membrane.
This force applies to the osmotic process in a reverse way. For this reason it is called the
reverse osmosis system. Figure 5 shows the reverse osmosis working principal. After
treatment treated water is collected in clean tank and the contaminants washed way as reject
water (Dvorak, 2008).
16 Figure 5: Osmosis and reverse osmosis main working principal (HITACHI, 2012)
When reverse osmosis is used for water treatment, a portion of water passes through the
membrane. Sometimes water contains higher amounts of minerals than it did prior to entering the
system. If the minerals are soluble then they will pass through the membrane to the flash water.
Otherwise no soluble minerals may clog to membrane. Table 8 shows some substance that may
cause clogging (Dvorak, 2008).
Table 8: Problem that may arise during water treatment in reverse osmosis system (Fisher
et al., 2008).
Substances
Problem may arise when
Alkalinity
"If alkalinity exceeds 1000 ppm and the majority of the alkalinity is
due to carbonate rather than bicarbonate, materials could precipitate"
Barium
"If barium concentrations exceed 1.5 ppm, barite (barium sulfate)
precipitate may form"
"Water containing more than 50 ppm boron and an alkalinity of
greater than 1000 ppm may form precipitates"
Boron
Calcium and
Magnesium
"If the pH of the membrane water is greater than 10 and the combined
calcium and magnesium content exceeds 60 ppm, precipitates may
form"
17 Hardness
"Hardness is a measure of the combined total concentration of
calcium,magnesium, and strontium in water. If pH exceeds 10,
alkalinity
exceeds
500
ppm,
and
hardness
exceeds
150ppm,precipitatesmay form"
Iron and
Manganese
"Combined concentrations of iron and manganese greater than 25 ppm
can lead to formation of precipitates"
Silica
"The concentration of silica should be lessthan 100 ppm"
Sulfate
"If water has a pH greater than 10 and contains sulfate greater than 50
ppm, it may produce a precipitate"
7. Materials, methods and experimental design:
Arsenic (III) and arsenic (V) were mixed with Laboratory tap water and prepared arsenic
contaminated water. All experiments were implemented in the department of Mathematical
science and technology (IMT) and in the laboratory of Plant science (IPM) department
laboratory, Norwegian University of Life Science. Malthe Winje Company, Norway installed the
Reverse osmosis system. In the experiments all pipes were connected to the reverse osmosis
system, production water tank and reject water collection tank. Arsenic (III) and arsenic (V)
samples were prepared separately for each experiment. This experiments were divided into three
steps. The first step was designed for arsenic (V). Arsenic (V) sample was prepared by
Na2HAsO4×7H2O (Sodium Hydrogen arsenat hepta hydrate, 98%) case number -10048-95-0,
formula weight-312.01 g/mole. In this experiment 500 liters arsenic (V) sample was prepared in
two different concentrations 200 µg/l and 50 µg/l (Arsenic mixed with water), in two different
pH condition pH=6 and pH=8. we calculated pressure for reverse osmosis system in production
water flow rate (l/h), two production water flow rate were applied 50 l/h and 200 l/h. Arsenic
sample were prepared in tank and adjusted so that the water was at pH=6 and pH=8 according to
experimental design. The pH was adjusted by Nitric acid (HNO3) and Sodium Hydroxide
(NaOH). Table 11 shows the experimental design for arsenic (V).
18 Table 11. Experimental design for arsenic (V):
Initial arsenic
sample water (l)
Arsenic concentration
(µg/l)
500
50
Flow rate in RO
system
(l/h)
50
500
50
500
pH
Sampling
time (min)
6
20
40
50
8
20
40
50
200
6
20
40
500
50
200
8
20
40
500
200
50
6
20
40
500
200
50
8
20
40
500
200
200
6
20
40
500
200
200
8
20
40
In this experiment arsenic contaminated water was treated by the reverse osmosis system.
Treated water was collected in plastic tubes for further analysis by Inductively Coupled Plasma
Mass Spectrometry (ICP-MS). Sixteen samples were taken from treated water and eight samples
were taken for initial concentration measurement and also reserve samples were taken from
every experiment. In the beginning of the treatment when the reverse osmosis system was started
this time first five minutes
were taken for reverse osmosis system flushed by arsenic sample
water, After cleaning, arsenic contaminated reject water was collected in tank for treatment by
K2S (Potassium sulfide).
19 Figure 6: Picture of reverse osmosis system and Treated water collection tube for ICP-MS
analysis.
The second step of the experiment was designed for arsenic (III). Arsenic (III) samples were
prepared by Na2AsO2 (Sodium arsenite solution containing arsenic trioxide, 100%) 0.05 mol/l
(0.1N). In the experiment 500 liters arsenic (III) sample was prepared in two different
concentrations 200 µg/l and 50 µg/l (Arsenic mixed with water), at two different pH conditions
pH=6 and pH=8. In the reverse osmosis system two production water flow rate were applied (50
l/h and 200 l/h). Arsenic contaminated water was adjust pH=6 and pH=8 according to
experimental design. The pH was maintained by Nitric acid (HNO3) and Sodium Hydroxide
(NaOH).
20 Table 12. Experimental design for arsenic (III):
Arsenic sample
Arsenic
Flow rate in RO
water (l)
concentration
system
(µg/l)
(l/h)
500
50
50
pH
Sampling
time (min)
6
20
40
500
50
50
8
20
40
500
50
200
6
20
40
500
50
200
8
20
40
500
200
50
6
20
40
500
200
50
8
20
40
500
200
200
6
20
40
500
200
200
8
20
40
In these experiments all steps were the same as the first step of experiment. After treating,
arsenic (III) contaminated water sample was taken for ICP-MS analysis. Sixteen samples were
taken from treated water and eight samples for initial concentration measurement and reserve
sample taken from every experiment. Reject water was collected in a tank for treatment by K2S
(Potassium sulfide).
21 Figure 7: Arsenic contaminated reject water collection tank.
After finishing two steps experimented water samples were analyzed by ICP-MS, According to
the results, arsenic concentration in treated water was different for Arsenic (V) and Arsenic (III).
Arsenic (V) treated water concentration was less than 1µg/l, This concentration is accepted
according to the WHO limit. The reverse osmosis system showed almost 99% removal efficiency
for arsenic (V) but the arsenic (III) concentration in treated water is higher than the WHO
guideline, the highest removal efficiency for arsenic (III) was (80%) and not suitable for drinking
water as per WHO guidelines. Therefore we decided on a new research plan for arsenic (III). In
this step we prepared arsenic (III) solution like before. We prepared 500 liters of arsenic
contaminated water for each experiment. In this step arsenic concentration was 200 µg/l, 50 µg/l
and 300 µg/l. we applies three pH condition pH=6, pH=8 and pH=10, Production water flow rate
in the reverse osmosis system was 200 l/h previous results show that a water flow rate 200 l/h is
better than 50 l/h. In this experiment arsenic (III) contaminated water passed through reverse
osmosis system twice. The first time arsenic contaminated water passed through the membrane
with one pH and a production water flow rate 200 l/h. After treatment pH was adjusted to initial
pH conditions and two different production water flow rate 200 l/h and 50 l/h. All arsenic
contaminated water was treated by the reverse osmosis system two times. We collected water in
plastic tubes for ICP-MS further analysis.
22 Table 13. Experimental design for arsenic (III) second step:
Arsenic sample
water (l)
Arsenic
concentration
(µg/l)
pH
Adjust
pH after
RO1
Water flow
rate in RO
system (l/h)
Sampling
time(Min)
6
Water flow
rate in RO
system
(l/h)
200
500
50
6
200
50
20
40
500
50
8
200
8
200
50
20
40
500
200
6
200
6
200
50
20
40
500
200
8
200
8
200
50
20
40
500
200
10
200
10
200
50
20
40
500
300
10
200
10
200
50
20
40
7.1 Description of membrane that use in experiment
Membrane company name: DWO FLIMTEC Membranes.
Membrane brand name: DOW FLIMTEC BW30-4040.
Table 9.Product specification:
Product
BW30-4040
Part number
80783
Feed spacer tick
Permeat flow
Stabilized salt
ness (mil)
rate gpd (m3/d)
rejection (%)
34
2400(9.1)
99.5
1. Permeate flow and salt rejection based on the following test conditions: 2,000 ppm NaCl,
applied flow rate: 150 psig (10.3 bar) for LE-4040 and 225 psig (15.5 bar) for BW304040 and BW30-2540, 770F (220C) and 15% recovery.
2. Permeate flows for individual elements may vary +/- 20%.
23 3. For the purpose of improvement, specifications may be updated periodically.
Table 10. Operating limit of the reverse osmosis system.
Polyamide Thin-Film Composite
Membrane type
1130F(450C)
Maximum Operating Temperature
Maximum operating pressure
600 psi(41 Bar)
Maximum feed flow rate 4040 elements
16gpm(3.6m3/h)
Maximum pressure drop
15psi(I Bar)
pH range continuous operation
2-11
pH range short time cleaning
1-13
Maximum feed silt density index
SDI5
Free chlorine tolerance
<0.1ppm
7.2 Statistical analysis
Minitab 16 was used for statistical analysis. A generalized linear model (GLM) from Analysis of
variance (ANOVA) test with 95% significant level was tested for the treatments for all the
parameters. The variables involved in this test were arsenic water concentration, reverse osmosis
production water flow rate, and arsenic contaminated water pH.
7.3 Materials use for experiment
The reverse osmosis system with connecting pipe , Sodium arsenate solution, sodium hydrogen
arsenate hepta hydrate, two 500 litres capacity tanks, Nitric acid, sodium hydroxide, pH meter,
Rapid chemical mixer, 16 watt electric cable. Plastic tube, ICP-MS,
24 8. Results
According to ICP-MS results for arsenic (V) concentration in treated water, we found 99%
removal efficiency in several treatment applications. (Appendix A) shows the treatment
efficiency in different treatment applications. Eleven treatment applications show the highest
removal efficiency (99%), and the lowest removal efficiency was 95%. Arsenic concentration in
treated water is acceptable according to WHO guidelines.
A significant relationship was seen between treated water arsenic (V) concentration pH and
water flow rate, No significant relationship was found with initial concentration of arsenic (V).
Table 14. Arsenic concentration with three treatment factors.
Factor
Sample
Mean±SD
DF
CV
F
Number
Concentration
16
125±77
1
61.97
0.54
pH
16
7 ±1
1
61.97
6.66
Water flow rate
16
125±77
1
14.75
7.99
2
All values are mean ± SD and significant level measure at p<0.05. R =55.9%, n=16
P
0.475
0.024
0.015
A significant relationship was obtained with pH and treated water concentration (P<0.05), and
also pH with water flow rate (P<0.05). However initial arsenic concentration and treated water
concentration was not significant (Table 14).
Figure 8 shows the percentage of efficiency in two pH conditions with two different water flow
rate. Sampled water at pH=8 showed a higher percentage of removal efficiency than sampled
water at pH=6. Water flow rate 200 l/h is more efficient than water flow rate 50 l/h. Each sample
number shows the removal efficiency of two pH and one water flow rate condition.
25 Flow rate (l/h)
pH= 6
pH= 8
Pressure,%of efficiency in two pH
200
150
100
50
0
1
2
3
4
5
6
7
8
Sampling number
Figure 8: Arsenic (V) percentage of removal efficiency (pH=6, pH=8) at two different flow rates.
Figure 9 shows the removal efficiency in two sampled waters at two different pH. Each sample
number shows the percentage of removal efficiency rate of two pH condition.
pH= 6
pH= 8
% of efficiency
100
98
96
94
92
90
1
2
3
4
5
Sample number
Figure 9: Arsenic (V) removal efficiency at pH=6 and pH=8 level.
26 6
7
8
In the experimental design two sets of experiments were performed for arsenic (III). Four
treatment conditions had the highest removal efficiency of 80% and one had the lowest (54%)
removal efficiency (Appendix B). Sixteen different treatment applications were performed.
A significant relationship was obtained between treated water arsenic (III) concentration, initial
concentration and water flow rate. No significant relationship was found between pH and treated
water concentration.
Table 15. Treated water arsenic concentration tested with three treatment factors.
Factor
Number
Mean±SD
DF
CV
F
Concentration
16
125±77
1
61.97
139.21
pH
16
7±1
1
61.97
1.78
Water flow rate
16
125±77
1
14.75
20.69
All values are mean ± SD and significant level measure at p<0.05. R2=93.09%, n=16
P
0.000
0.207
0.001
A significant relationship was found (P<0.05) with initial arsenic (III) concentration and treated
water arsenic (III) concentration. A significant relationship with water flow rate and treated
water concentration was also found, (P<0.05). No significant relationship was observed with pH
and treated water arsenic concentration (Table 15).
Figure 10 shows the percentage of arsenic (III) removal efficiency in two pH conditions with two
different water flow rate. Water flow rate at 200 l/h was more efficient than water flow rate at 50
l/h. Each sample number shows that removal efficiency of two different pH and one water flow
rate condition.
27 Flow rate (l/h)
pH =8
pH =6
Pressure,%of efficiency in two pH
200
180
160
140
120
100
80
60
40
20
0
1
2
3
4
5
Sample number
6
7
8
Figure 10: Removal efficiency of arsenic (III) percentage in pH=6 and pH=8, two different flow
rates.
Water flow rate at 200 l/h showed more removal efficiency than water flow rate at 50 l/h, treated
water arsenic (III) concentration depends on initial arsenic (III) concentration. Figure 11 shows
the removal efficiency of two different water flow rate.
Flow rate 200 l/h
Flow rate 50 l/h
% of efficiency
100
80
60
40
20
0
1
2
3
4
5
Sample number
6
Figure 11. Arsenic (III) removal efficiency of two different water flow rates.
28 7
8
In the last step we performed two times treatment for arsenic (III). Highest removal efficiency
was found in sample water at pH=10 condition. 99% removal efficiency was found in pH=10
level and lowest removal efficiency was found at pH=6 condition. (Appendix C)
We observed highest (99%) removal efficiency and lowest (76%) removal efficiency. In the first
step flow rate was fixed for treatment.
Results showed a significant relationship of treated water arsenic (III) concentration with initial
concentration and pH. There is no significant relationship between water flow rate and treated
water arsenic concentration.
Table 16. Arsenic concentration shows with three treatment factors.
Factor
Number Mean±SD
DF
CV
F
Concentration
10
140±77
1
55.33
23.55
pH
10
7.6±1.57
2
20.76
12.31
Water flow rate
10
125±79
1
63.25
5.16
2
All values are mean ± SD and significant level measure at P<0.05. R =88.86%, n=10
P
0.005
0.012
0.072
A significant relationship was found with Initial concentration and treated water concentration
(P<0.05). On the other hand there is no significant relationship with water flow rate. Figure 10
shows the percentage of arsenic (III) removal efficiency in three different pH conditions. Water
at pH=10 condition had a better removal efficiency compared to the other two pH.
pH6
pH8
pH10
100
%of efficiency
80
60
40
20
0
1
2
3
Sample number
Figure 12: Arsenic (III) removal efficiency in three different pH conditions.
29 4
Figure 13 shows that removal efficiency was calculated with combined removal % of reverse
osmosis 1 (RO1) and reverse osmosis 2 (RO2). While pH=10
RO1 efficiency is higher than
RO2 compared to other pH condition. Each sample number represents combined arsenic (III)
% of removal efficiency RO1 and RO2
removal efficiency.
Combined removal % from RO1 and RO2
100
90
80
70
60
50
40
30
20
10
0
1
2
3
4
5
% of removal from RO2
36
44
64
43
14
% of removal from RO1
55
49
23
49
85
Figure13: The combined removal percentage of arsenic (III) RO1 and RO2.
9. Discussion
Our results suggest that the reverse osmosis system is significant to remove arsenic from
drinking water. The reverse osmosis system and the membrane are very efficient for removing
arsenic from drinking water. Removal efficiency level was 99% for arsenic (V) and 99% for
arsenic (III) in different treatment applications.
Arsenic concentration is responsible for removal efficiency of arsenic (III) compared to arsenic
(V). There are no statistically significant relationships with removal efficiency of arsenic (V).
Arsenic (III) is more soluble and neutral charged in water. Arsenic (V) is negatively charged and
less soluble in water. Arsenic (III) also becomes charged with higher pH condition. Arsenic (V)
feed water concentration used 2000 µg/l and arsenic (III) used different concentration for
treatment and pre oxidation process recommended for better removal efficiency (Geucke et al.,
30 2008). Organic carbon, chlorine, Monochloramine, potassium permanganate used for pre
oxidation (Ning, 2002). In our experiment we got very good efficiency rate for arsenic (III)
without any pre oxidation step. Further research is needed to investigate higher concentration
removal efficiency.
Production of water by the reverse osmosis system depends on production water flow rate.
Removal efficiency is higher for arsenic (III) and arsenic (V) at higher production water flow
rate. Production water flow rate is more significant for arsenic (III) efficiency rate compared to
arsenic (V).
Removal efficiency is also dependent on in arsenic contaminated water pH. The pH has
significant effects on removal efficiency from water. Different pH conditions have different
removal efficiencies. According to the experiments, arsenic (III) removal is more depended on
pH than arsenic (V). That gradually increases pH in contaminated water and gradually increases
removal efficiency. Experiments show solution pH affects the removal of arsenic (III) because
most of the arsenic (III) exists in monovalent anion from pH=10, while most of the arsenic (III)
exists in a neutral molecule at pH=6 and pH=8. The pH range was applied from 3 - 10 for arsenic
(III) removal in two different membranes (Kang, 2000), For ES-10 membrane removal efficiency
was 75% and NTR-729HF membrane removal efficiency was 43%. In our experiment arsenic
(III) removal efficiency was 99% in pH=10 condition with BW30-4040.
Studies report arsenic removal ranging between 40-90% without specifying the arsenic species
removed (Gomez-Caminero et al., 2001). Another pilot study reported arsenic (V) removal at 9699% and arsenic (III) removal at 46-84%. A second pilot study (Gomez-Caminero et al., 2001)
reported that arsenic (III) reduction at 73%, Bench – scale studies with reverse osmosis
membrane shows arsenic (V) reduction at 88-96% and arsenic (III) reduction at only 5%.
In our experiment arsenic removal rate is more than 99% from 400 µg/l for both arsenic (III)
and arsenic (V). The DOW FILMTEC (BW30-4040) membrane is efficient for arsenic removal
from drinking water. This membrane has also removed other ions from drinking water. It may
prove efficient at removing heavy metals from waste water and removing harmful
microorganisms from drinking water. Further research is needed in this regard.
31 10. Conclusions
Arsenic rejection is significantly higher from the contaminated water. Arsenic (V) and arsenic
(III) were very efficiently removed by reverse osmosis. The removal of arsenic was strongly
affected by the solution pH, especially arsenic (III). Two time’s arsenic contaminated water pass
through the membrane and the removal efficiency rate 99%. When dealing with ground water
high values of arsenic (III), a higher pH adjustment might be recommended. It was demonstrated
that pH control for sample water is essential for the successful removal of arsenic compounds.
Practical processes can be developed with reverse osmosis to remove all major species of arsenic
from drinking water. Further studies are needed in the characterization of the Arsenic species
being treated and in preparing a suitable design of the reverse osmosis process to match the
demand. Reverse osmosis systems can produce safe drinking water for arsenic affected areas all
over the world.
32 References
CHEN, C. L., HUS, L. I., CHIOU, H. Y., Y.M., H., CHEN, S. Y., WA, M. M. & CHEN, C.
2004. Ingestion arsenic , cigarette smoking, and lung cancer skin, a flow up study in
arsenicosis" endomic area in Taiwan. JAMA, 292, 2984-2990.
CHOONG, T. S. Y., CHUAH, T. G., ROBIAH, Y., KOAY, F. L. G. & AZNI, I. 2007. Arsenic
toxicity, health hazards and removal techniques from water: an overview. Desalination,
217, 139–166.
DHARMAPPA, H. B. & HAGARE, P. 1999. Economic analysis and design of crossflow
microfiltratiofor water treatment systems. Desalination, 121, 1-11.
DVORAK, B. I. 2008. Drinking water treatment reverse osmosis [Online]. University of
Nebraska.
Available:
http://www.ianrpubs.unl.edu/epublic/live/g1490/build/g1490.pdf?mobile=no [Accessed
13.03. 2012].
FISHER, A., POWELL, J. R. P. & WALKER, M. 2008. Reverse Osmosis (R/O):How It Works
[Online]. University of navada. [Accessed 13.03. 2012].
GARELICK, H. & JONES, H. 2008. Mitigating arsenic pollution: bridging the gap between
knowledge
and
practice
[Online].
Chemistry
International.
Available:
http://www.iupac.org/publications/ci/2008/3004/2_garelick.html [Accessed 13.03. 2012].
GEUCKE, T., DEOWAN, S. A., HOINKIS, J. & PATZOLT, C. 2008. Performance of a smallscale RO desalinator for arsenic removal. Desalination, 239, 198-206.
GOMEZ-CAMINERO, A., HOWE, P., HUGHES, M., KENYON, E., LEWIS, D. R., MOORE,
M., NG, J., AITIO, A. & BECKING, G. 2001. Environmental Health Criteria 224:
arsenic and arsenic compounds [Online]. Geneva: WHO. Available:
http://www.inchem.org/documents/ehc/ehc/ehc224.htm [Accessed 12.03. 2012].
HANK, M. & WYCKOFF, D. 2010. Ultrafiltration in Decentralized Water Treatment
Application
[Online].
Spotlight.
Available:
http://www.wcponline.com/pdf/1004Hank_Wycoff.pdf [Accessed 10.03. 2012].
HITACHI.
2012.
Environmental
acivities
[Online].
Japan.
Available:
http://www.hitachi.com/environment/showcase/solution/industrial/desalination_plant.htm
l [Accessed 14.03. 2012].
HOPENHAYN-RICH, C., BIGGS, M. L. & SMITH, A. H. 1998. Lung and kidney cancer
mortality associated with arsenic in drinking water in Córdoba, Argentina. Int J
Epidemiol. , 27, 561-579.
33 JI, Q. A. Y., ZHAOB, Q., CHENA, H. & GAOA, C. 2011. Preparation of novel positively
charged copolymer membranes for nanofiltration. Journal of Membrane Science, 376,
254–265.
KANG, M. 2000. Effect of pH on the removal of arsenic and antimony using reverse osmosis
membranes. Desalination, 131, 293-298.
MANDAL, B. K. & SUZUKI, K. T. 2002. Arsenic round the world: a review. Talanta, 58, 201235.
NGUYEN, V. T. 2007. Arsenic removal by a membrane hybrid filtration system. Desalination,
236, 363-369.
NING, R. Y. 2002. Arsenic removal by reverse osmosis. Desalination, 143, 237-241.
ROSSMAN, T. G., UDDIN, A. N. & BURUN, F. J. 2004. Evidence that arsenic acts as a cocar
cinogan in skin cancer. Toxicol., 198, 394-404.
SAFIUDDIN, M. 2001. Ground water arsenic contamination in bangladesh: causes, effects and
remediation. Proceedings of the 1st international conference and 7th annual paper meet,
Bangladesh. Chittagong, Bangladesh: Institute of Engineers.
SAHA, P. R. 2002. Metabolism and toxicity of arsenic: A human carcinogen. Current Science,
82, 38-45.
SEGAL, Y. & DOSORETZ, C. G. 2011. Quantitative estimation of protein fouling of ultrafiltration membranes by photoacoustic spectroscopy. Desalination, 271, 231–235.
WASSERMAN, G. A., LIU, X., PARVEZ, F., AHSAN, H., FACTOR-LITVAK, P.,
VANGEEN, A., SLAVKOVICH, V., LOIACONO, N. J., CHENG, Z., HUSSAIN, I.,
MOMOTAJ, H. & GRAZIANO, J. H. 2004. Water arsenic exposure and children’s
intellectual function in Araihazar, Bangladesh. Environ. Health Perspect, 112, 1329–
1333.
ZÜRICH, B. M. 2007. Arsenic contamination of groundwater and drinking water in the red river
delta, Vietnam: geochemical Investigations and mitigation measures. PhD, University of
Karlsruhe.
34 Appendix index
Appendix A. Table shows the arsenic (V) concentration in treated water and % of
removal efficiency.........................................................................................................
Appendix B. Table shows the arsenic (III) concentration in treated water and % of
removal efficiency…………………………………………………………………….
Appendix C: Table shows the arsenic (III) concentration in treated water and % of
removal efficiency after two times treated by Reverse osmosis system……………..
35 Appendix
Appendix A. Table shows the arsenic (V) concentration in treated water and % of removal
efficiency.
Initial arsenic
concentration
(µg/l)
50
50
Water pH
flow rate
(l/h)
50
6
50
6
Sampling
time (min)
Arsenic concentration in
treated water (µg/l)
% of efficiency
20
40
1
1.6
98
96
50
50
50
50
8
8
20
40
<0.5
<0.5
99
99
50
50
200
200
6
6
20
40
0.7
<0.5
99
99
50
50
200
200
8
8
20
40
<0.5
<0.5
99
99
200
200
50
50
6
6
20
40
1.4
2.4
97
95
200
200
50
50
8
8
20
40
<0.5
0.6
99
98
200
200
200
200
6
6
20
40
<0.5
0.6
99
99
200
200
200
200
8
8
20
40
<0.5
<0.5
99
99
36 Appendix B. Table shows the arsenic (III) concentration in treated water and % of removal
efficiency.
Initial arsenic
Concentration
(µg/l)
50
50
Water
flow rate
(l/h)
50
50
pH
Sampling
time(min)
Arsenic concentration in
treated water(µg/l)
% of removal
efficiency
6
6
20
40
23
26
54
48
50
50
50
50
8
8
20
40
17
19
66
62
50
50
200
200
6
6
20
40
10
14
80
72
50
50
200
200
8
8
20
40
10
13
80
74
200
200
50
50
6
6
20
40
73
82
63
59
200
200
50
50
8
8
20
40
63
68
68
66
200
200
200
200
6
6
20
40
39
57
80
71
200
200
200
200
8
8
20
40
40
55
80
72
37 Appendix C: Table shows the arsenic (III) concentration in treated water and % of removal
efficiency after two times treated by Reverse osmosis system.
Arsenic
concentra
tion
(µg/l)
50
pH
Adjust pH
after RO1
Water
flow rate
unit (l/h)
6
Water
flow rate
in RO unit
(l/h)
200
6
50
8
200
200
6
200
% of removal
efficiency
200
50
As(III)
concentration
in treated water
(µg/l)
4.1
8.9
8
200
50
3.2
7.7
93
84
200
6
200
50
24
48
88
76
8
200
8
200
50
16
32
92
84
200
10
200
10
200
50
0.5
1.5
99
99
300
10
200
10
200
50
0.5
1
99
99
38 91
82